Ingeniero

4/16/2012

Static pressure




Static pressure in a tunnel-ventilated house static is primarily an indicator of how hard the exhaust fans are working. High pressure - high work level
 

high level of fan restriction reduced air moving capacity…reduced cooling minimum fan restriction maximum air flow...maximum cooling

Tunnel Ventilation and Static Pressure
Michael Czarick TheUniversity of Georgia



Low pressure - low work level
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Fan output Vs. Static pressure
22,000 20,000 18,000 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0
0 0.02

How does static pressure affect a our ability to cool birds?

Cfm

Pressure

Cfm

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2

0.22

0.24

Static Pressure

40’ X 500’ droppedceiling house
(Ten fans, cross-sectional area = 370 ft2)
  

0.26

Wind-chill effect at 85oF
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0 50 100 150 200 250 300 350 400 450 500 550 600 Air Velocity (ft/min)

22,000 20,000 18,000 18 000 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0
0.02 0.04 0.06 0.08 0.12 0.14 0.16 0.18 0.22 0.24 0.26 0 0.1 0.2

Static Pressure

Wind Chill (F)C

0.05” fan capacity=20,000 cfm air velocity =540 ft/min

  

0.15” fan capacity=16,500 cfm air velocity = 445 ft/min

Cfm

1

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550 ft/min
100.0°F 100

Wind-chill effect at 85oF
16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 0
70.0°F

90
78.9 85.1

80

Wind Chill (F) C

50

100 150 200 250 300 350 400 450 500 550 600 Air Velocity (ft/min)

350 ft/min100.0°F 100

Static pressure can also affect air exchange rates


Lower air exchange, greater temperature differential.

Low pressure
90
80.0 89.2

80

High pressure
70.0°F

40’ X 500’ dropped ceiling house
(ten fans, cross-sectional area = 370 ft2)
    

High static pressure can result in increased air leakage…further increasing temperature differentials
80.0°F 80

0.05”fan capacity=20,000 cfm air velocity =540 ft/min wind chill = 12oF temp diff = 5oF

    

0.15” fan capacity=16,500 cfm air velocity = 445 ft/min wind chill = 8oF temp diff = 6oF

70

60

50

40.0°F

2

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High static pressure =lower air velocities leading to more trapped heat between birds
100.0°F 100

High static pressure = lower air velocities which can makehigh Rh more of a problem
80% 70%
95

60% 50%

90

40% 30%

respiration air

85

20% 10%

80 78.0°F

0% 100 200 300 400 500 600

To optimize fan performance…
(air velocity and exchange)


What creates work/pressure for the tunnel fans?


We would like to keep static pressure as low as practically possible.

There are basically four areas in a poultry house that cancause an increase in the static pressure the fans are working against:

Areas of work
1) 2) 3) 4)

Tunnel inlet area
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Tunnel inlet area Between inlet and exhaust Exhaust – shutters/light traps External – wind or hoods
3

Two factors that determine the amount of work required to pull air into a house
 

Amount of inlet opening What is in the inlet opening (i.e., pads, light traps)1

2

4

3

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Relationship between tunnel inlet opening and static pressure


Relationship between tunnel inlet speed and static pressure
Air Velocity 0.07
p static pressure (")

Decrease the amount of opening
 

air speed at the inlet increases static pressure increases air speed at the inlet decreases static pressure decreases

Static Pressure

Work

0.060.05 0.04 0.03 0.02 0.01 0
100 150 200 250 300 350 400 450 500 550
air velocity



Increase the amount of opening
 

40’ X 500’ house with 200,000 ft3/min of tunnel fan capacity (no end wall)
   

40’ X 500’ house with 200,000 ft3/min of tunnel fan capacity (no end wall)
    

Opening

= (8’ + 11’)/2 X 40’ = 9.5’ X 40’ = 380 ft2 Entrance speed?????

Opening...